1. Field of the Invention
The invention relates generally to retread tires and more specifically, to retreaded tires having tread bands with grooves open to the front face and grooves open to the back face of the tread band.
2. Description of the Related Art
When tires become worn, they can be restored with new tread. Large truck tires and bus tires, for example, are typically retreaded as part of a routine tire-management program. The carcass of these types of tires is expected to last several hundred thousand miles and be amenable to having a new tread adhered to it several times. Such tires are quite expensive and are therefore bought with the expectation that their high initial costs are offset by the long service life of the carcass and the low comparative cost of retreading. Indeed, the economics included in the selection and purchase of such tires often dictate that the original tires be capable of being retreaded as many as three or four times or more.
A variety of procedures and different types of equipment are available for use in recapping or retreading pneumatic tires. One of the first steps in retreading a worn tire is to remove remaining tread material from the tire carcass, for example, by a procedure known as buffing. Next a layer of green (uncured) rubber, known as “cushion gum,” may be applied to the carcass. This layer of uncured rubber may be extruded directly onto or rolled (stitched) onto the carcass. Next, a tread band is applied atop the layer of cushion gum.
In the cold recapping process, the tread band is cured rubber, and has a tread pattern already impressed in its outer and/or inner surfaces. Such precured bands, as the term is used herein, refer to tread bands that have been cured either fully or to some lesser extent but have undergone to some extent some level of curing. The tire is then placed in an autoclave, and heated under pressure for an appropriate time to induce curing of the gum layer, and bonding of the gum layer to the tread and the carcass.
In the hot recapping process, the tread is uncured rubber and typically may have no or very little tread pattern when initially placed on the tire carcass. The tire with the uncured tread is placed in a tire mold and heated under pressure for an appropriate time to cure the gum layer and the tread, to mold the tread with the desired tread pattern, and to cause the gum layer to bond with the tread and the carcass. The term “cure” refers to the formation of cross-links between the elastomer molecules in the rubber compound, otherwise known as vulcanization.
Buffing the old tread off of the tire in preparation of the retreading process removes rubber that is discarded as waste. Much of this waste rubber that is removed in preparation of retreading is typically replaced during the retreading process as part of the undertread portion of the tread band that is bonded to the carcass during retreading. It would be advantageous if the amount of rubber that is discarded is reduced.